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cancer, tissue renewal, stem cells and stem cell therapies (Stem cell…

- - - - excess growth of cells within their original tissue
    - - malignant tumour
      - damage may be life threatening
      - cells break through boundaries
      - enter bloodstream
      - formation of metastases
  - - - anti-proliferative genes
      - are inactivated in cancer
      - in normal cell proliferative protein is inactivated by tumour suppressor
      - in cancerous cell proliferative protein is not inactivated by tumour suppressor
      - example of a tumour suppressor
        
        p53
        
        indirect mechanism = activation of p53 activates transcription of genes whose proteins will arrest cell cycle
    - - proliferative genes
      - are activated in cancer
      - in normal cell
        
        the intracellular signalling proteins are activated only if growth factor binds to receptor
        
        signalling proteins activate gene regulatory protein which activates transcription of gene required for cell proliferation
      - in cancerous cell
        
        intracellular signalling proteins are abnormally activated
      - example of proto oncogene
        
        Ras
- - - - early zygote cells can give rise to all cell types
        
        embryo
        
        placenta
        
        extra-embryonic membranes
      - cells up to 8-cell stage of mouse development retain this capability
    - - blastocyst cells of the inner mass can give rise to embryonic cell types
    - - bone marrow stem cells can give rise to all blood cell types
      - all blood cells come from a single type of hemapoietic cell in bone marrow
      - can give rise to
        
        T lymphocyte
        
        B lymphocyte
        
        monocyte
        
        red blood cell
        
        and more
    - - gut epithelial stem cells
        
        single cell layer
        
        folded into crypts and villi
        
        stem cells reside at the base of the crypt
        
        dividing precursor cells in the middle of the villi
        
        differentiation into various secretory and absorbative cell types
        
        small intestine
        
        cells need to be continuously replaced due to to loss at the tips of villi #
      - give rise to a few terminally differentiated cell types
    - - stem cells in basal epidermis give rise to skin keratinocytes
      - epidermis
        
        the pattern of cell renewal varies according to tissue organisation
        
        1) basal cells (including stem cells and dividing precursors)
        
        divide 2-3 times before they start to differentiate
        
        start losing expression of cell adhesion molecules specific to basal layer
        
        start gaining expression of adhesion molecules
        
        2) cells are pulled in the suprabasal layer
        
        lose capacity to divide
        
        3) cells continue to move upwards
        
        become flattened
        
        become dehydrated
        
        nucleus and other contents are broken down
        
        4) cells are sloughed off at the surface
- - - - avoid problems of immune rejection
      - avoid ethical questions